Why would you think that? No two months of manufacturing this car have ever been like the prior two. I doubt this will stabilize to any consistent pattern until next year. I would imagine they meet weekly, if not daily, and are constantly revising production plans several weeks out based on orders in queue, material supply chain delivery, labor, etc.
For several reasons:
1. They have over 450,000 reservations (Yes I know this is a global number, but at least 1/3 to 1/2 of those are in the US and Canada). They probably have somewhere on the order of 60-80,000 configured orders judging from the delta between orders and deliveries/non deliveries (e.g. My 8+ weeks so far). This should give them ample visibility on near-term demand, in addition to the non binding preferences reservation holders can indicate prior to configurating. This means they know, for example that they have to produce 20K MSM, 15K MCR, 10K MCW, 5K OBM, etc. They also know from the configured order queue what the ASP per batch is and can prioritize higher margin production first and lower later (within reason).
2. There are only so many possible configurations and even fewer differing hardware components which means supplier constraints likely to be very minimal issue if at all. At present, cars physically only differ in (1) wheel size, (2) RWD/AWD, (3) exterior color and (4) interior color. Everything else is exactly the same. Same door handles. Same rear motor. Same sound system. Same touch screen. Same steering wheel. Same same same. You get the idea. It seems to be the exterior paint color that drives batching given the paint shop is the current production bottleneck.
3. Given (1) and (2), they should have a general idea of when John Smith's car will be built. For example, if John ordered a MSM AWD with aeros, Tesla should know that with current paint batching and production plans that configuration is scheduled to run on the production line in week 11 putting his car roughly between October 30-Nov 7. The level of precision here is higher than a 3-month/13 week window. If you're suggesting that tesla just plans their production runs one week out then, if true, Tesla has some even bigger production problems on their hands. I have a couple of very good friends who work in consumer product manufacturing (one of whom is at a very well known consumer electronics company that just opened a spaceship campus) and both have told me production runs are pretty well planned out months ahead of time based on expected consumer demand data (e.g. color mix, storage capacities etc).
As an aside, when my first EV was built back in 2011, I was given a two week window when my car would be coming off the assembly line and a 3-4 week window for delivery based on transportation logistics. That was from a startup company that many would say (myself included) had far worse operations and technical management. And true to form, I got my car at the far end of that 4 week window. There were 3 trims, 7 exterior colors and 8 (I think) interior color choices.